1. Field of the Invention
The present invention relates to a method of growing high quality silicon single crystal, and more particularly, to a method and apparatus of growing a high quality silicon single crystal ingot by controlling temperature distribution of silicon melt during Czochralski growth of silicon single crystal, and silicone wafer fabricated thereby.
2. Description of the Related Art
As well known in the art, in order to grow a high quality silicon (Si) single crystal ingot that can enhance semiconductor device yield, temperature control has been conducted on high temperature distribution of the single crystal ingot mainly after crystallization. This methodology is intended to control stress that may be induced from contraction owing to cooling subsequent to crystallization or by the behavior of point defects built up in solidification.
According to a typical process of Czochralski growth of Si single crystal, polycrystalline Si is loaded into a quartz crucible where it is melted into Si melt under the heat radiated from a heater, and then a Si single crystal ingot is grown from the surface of Si melt.
When growing the Si single crystal ingot, the crucible is elevated through the rotation of a shaft that supports the crucible, maintaining the solid-liquid interface to a constant level, and the Si single crystal ingot is wound up as rotated coaxially with the crucible but in reverse direction.
Generally, for the purpose of efficient growth of the Si single crystal ingot, inert gas such as argon Ar is blown into an ingot-growing apparatus via an upper portion thereof and exhausted from the ingot-growing apparatus via a lower portion thereof.
Conventional techniques for growing a Si single crystal ingot as above have used a heat shield and a water cooling pipe in order to control the temperature gradient of a growing Si single crystal. Examples of such conventional techniques include Korean Patent No. 374703, Korean Patent No. 0411571 and U.S. Pat. No. 6,527,859.
However, controlling the temperature gradient of single crystal is, by itself, not sufficient to manufacture a high quality Si single crystal ingot and a Si wafer having low point defect concentration.
In particular, in case of fabricating semiconductor devices from a Si wafer manufactured according to a conventional technique, micro precipitates are formed from point defects through repeated heat treatment in device fabrication. As a drawback, the micro precipitates cause faults, resulting in poor device yield.
As disclosed in U.S. Pat. Nos. 5,919,302, 6,287,380 and 6,409,826, the axial temperature distribution of crystal G0 is in the form of G0=c+ax2, making a tendency that vacancy concentration rises but interstitial concentration descends from the periphery to the center of a wafer. Unless sufficient out-diffusion takes place in vicinity to the wafer, interstitial crystal defects such as LDP occur. Subsequently, it is common practice to conduct crystal growth with high vacancy concentration in the center. Vacancy concentration, much higher than equilibrium concentration, tends to create vacancy-related crystal defects (e.g., void and Oxidation Induced Stacking Fault (OiSF)) in a central portion of the wafer. Besides, even though a void or OiSF region is controlled, micro precipitates may emerge from latent state through several heat treatments in semiconductor fabrication.
Other conventional techniques, which control the temperature distribution of single crystal in order to manufacture a high quality Si single crystal, are as follows: Japanese Patent Application No. Hei 02-119891 has been proposed to control the temperature distribution of the center and periphery of a Si single crystal ingot by adopting a hot zone during the cooling of the Si single crystal ingot in order to reduce lattice defects of the Si single crystal ingot owing to the strain of solidification. With this technique, in particular, the use of a cooling sleeve has enhanced solidification rate and reduced lattice defect in the growth direction of the Si single crystal ingot. Japanese Patent Application No. Hei 07-158458 has proposed to control the temperature distribution and the pulling speed of a crystal ingot, whereas Japanese Patent Application No. Hei 07-66074 has proposed to improve a hot zone and adjust cooling rate in order to control defect density. Japanese Patent Application No. Hei 04-17542 and U.S. Pat. No. 6,287,380 have proposed to change a hot zone and control cooling rate in order to restrict the formation of crystal defects by using the diffusion of point defects. Korean Patent Application No. 2002-0021524 discloses that improvement in a heat shield and a cooling pipe has enhanced the productivity of high quality single crystal. Japanese Patent Application Hei 05-61924 has proposed to periodically change the growth rate of crystal in order to utilize the hysteresis of a region having crystal defects such as OiSF and oxygen precipitation defect, thereby preventing crystal defects in a Si single crystal ingot.
However, these conventional techniques are based upon solid state reaction, and thus have the following problems: First, there are a number of hindrances to achieve an aim of high quality Si single crystal. For example, U.S. Pat. No. 6,287,380 is aimed to sufficiently diffuse supersaturated point defects in a high temperature region before growing them into crystal defects in order to drop point defect concentration. However, temperature has to be maintained up to 16 hours or more for this purpose, and thus this technique can be realized only theoretically but not in actual use.
Second, nearly all the conventional techniques have failed to have a practical effect. When a 200 mm diameter Si single crystal ingot was grown by periodically varying the pulling speed of the crystal ingot as proposed by Japanese Patent Application Hei 05-61924 and Eidenzon et al (Defect-free Silicon Crystals Grown by the Czochralski Technique, Inorganic Materials, Vol. 33, No. 3, 1997, pp. 272-279), aimed high quality was not achieved but stability in process was incurred to the contrary.
Third, those inventions based upon solid state reaction cannot achieve high productivity. Even though a heat shield and a water-cooling pipe were designed in optimal conditions according to the Korean Patent Application No. 2001-7006403, this arrangement merely showed low productivity and pulling speed for high quality single crystal was actually about 0.4 mm/min.
Another conventional technique for producing high quality Si single crystal is to control solid-liquid interface (crystal growth interface). Korean Patent Application No. 1998-026790 and U.S. Pat. No. 6,458,204 limit the profile of a solid-liquid interface for producing high quality Si single crystal. However, single crystal of sufficiently high quality was not produced in U.S. Pat. Nos. 5,919,302 and 6,287,380, even though they have a solid-liquid interface proposed by the above inventions.
Moreover, the foregoing conventional techniques showed low production yield in high quality single crystal.